Second director of the Courtauld Institute and scholar of the art of the Crusades. Boase was the son of Charles Millet Boase, a bleaching mill manager at near Dundee and Anne Malcolm Sherrer Ross. He attended Rugby School from 1912. A prize given for an essay on Lorenzo de' Medici led to a scholarship at Magdalen College, Oxford. At Oxford he studied under the historian Francis Fortescue Urquhart (1868-1934), known as "Sligger," whose method can be seen in Boase's own work.

Architectural historian and crusader for the protection of French medieval monuments; harsh opponent of Eugène Viollet-le-Duc's restorations.

Scholar of Romanesque sculpture and history of fortifications (Crusades). Deschamps was the leader in the nationalistic counter attack to the debate on the origin of the Romanesque. It had been launched by the American A. Kingsley Porter when he posited that pilgrimage and monastic reform explained the stylistic progress of the Romanesque, eminating not from France, but from Spain. The French academy rejected Porter's thesis in favor of their regional hierarchy.